Cathode ray tube implosion protection system and method

ABSTRACT

A glass cathode ray tube envelope is provided with implosionprotection means by wrapping the peripheral portion of the envelope adjacent to the faceplate with a piece of fabric impregnated with an uncured thermosetting bonding material (e.g., B-stage epoxy resin), positioning a first steel band around the tape, heating about two-thirds of the band to 200*-250* C., contacting the tape with the band while hot, to bond the tape to the glass envelope and band along about two-thirds of the periphery of the envelope, and tensioning and permanently mounting the band on the envelope by welding the ends together under tension while still hot so that, on cooling, the band tension is increased to a large value, e.g., 1,500 pounds, and then mounting a second steel band on the first band in the same manner as the first band but with the band joint on the opposite side of the envelope, to bond the tape to the envelope and first band along the remaining portion of the periphery thereof.

United States Patent Hildebrants 51 Oct. 10, 1972 [54] CATHODE RAY TUBE IMPLOSION PROTECTION SYSTEM AND METHOD [72] Inventor: Arnis Hildebrants, Jonesboro, Ind. [73] Assignee: RCA Corporation [22] Filed: Oct. 27, 1970 [21] Appl. No.: 84,413

[52] US. Cl ..178/7.82 [51] Int. Cl ..H01j 27/06 [58] Field of Search ..l78/7.8, 7.82

[56] References Cited UNITED STATES PATENTS 3,512,234 5/1970 Bongenaar et a1. 178/7.82 X 3,456,076 7/1969 Griswold et a1 ..178/7.82 3,573,368 4/1971 Kober l78/7.8 3,206,056 9/1965 Stel l78/7 82 X Primary ExaminerRobert L. Griffin Assistant ExaminerRichard K. Eckert, Jr. Attorney-Glenn H. Bruestle [5 7] ABSTRACT A glass cathode ray tube envelope is provided with implosion-protection means by wrapping the peripheral portion of the envelope adjacent to the faceplate with a piece of fabric impregnated with an uncured thermosetting bonding material (e.g., B-stage epoxy resin), positioning afirst steel band around the tape, heating about two-thirds of the band to 200250 C., contacting the tape with the band while hot, to bond the tape to the glass envelope and band along about two-thirds of the periphery of the envelope, and tensioning and permanently mounting the band on the envelope by welding the ends together under tension while still hot so that, on cooling, the band tension is increased to a large value, e.g., 1,500 pounds, and then mounting a second steel band on the first band in the same manner as the first band but with the band joint on the opposite side of the envelope, to bond the tape to the envelope and first band along the remaining portion of the periphery thereof.

3 Claims, 3 Drawing Figures YPATENTEDHBI 1 m2 3.697.686

//Vl ENT 0R I Z3 Arm's Hildebrants CATI'IODE RAY TUBE IMPLOSION PROTECTION SYSTEM AND METHOD BACKGROUND OF THE INVENTION In order to prevent or minimize the implosion of evacuated glass envelope cathode ray tubes due to atmospheric pressure on the viewing faceplate, such tubes are usually protected by either laminating a safety glass window to the faceplate, or surrounding the envelope adjacent to the faceplate with tension means which restrains the envelope against outward expansion. Laminated windows are undesirable since they are heavy and costly, and also are not as safe as other implosion protection systems.

One form of tension means that has proven satisfactory for small and medium tubes up to about 19V size (viewing diagonal dimension in inches) is the simple T-band type in which the envelope periphery is provided with one or more wrappings of cloth tape having a pressure type adhesive, and a steel tension band is mounted on the tape with a tension of several hundred pounds. However, attempts to use this type of implosion protection on tubes of larger size (20V and above) have been unsuccessful, even when two steel bands were used.

SUMMARY OF THE INVENTION The side wall of a glass cathode ray tube envelope adjacent to the faceplate is wrapped with a piece of fabric tape impregnated with a thermosetting bonding material, such as semicured epoxy resin; and a first steel band is positioned around the tape, heated by passing an electric current through the major portion thereof to a temperature sufficient to cure the bonding material, moved while hot into contact with the tape, to cure and bond the tape to the glass envelope and the band along the major portion of the tape, and then permanently mounted on the envelope by joining the ends together under tension while still hot, so that, on cooling, the band tension is increased to a relatively high value, preferably about l,500 pounds. Then, a second steel band is mounted on the first band, in the same manner as the first band but with the joint on the opposite side of the envelope, in order to cure'and bond the tape to the envelope and first band along the remaining portion of the tape.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an end view, looking toward the faceplate, of a cathode ray tube incorporating the present invention.

FIG. 2 is a side view, partly in axial section along line 2-2 of FIG. 1, of the tube of FIG. 1.

FIG. 3 is a partly schematic, plan view of an apparatus for mounting implosion protection means on a glass cathode ray tube envelope according to the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION In FIGS. 1 and 2, the numeral 1 designates a glass cathode ray tube having an envelope or bulb 2 of generally rectangular shape with opposite major sides Ia and opposite minor sides lb. The envelope 1 comprises a large cap or panel 3 sealed to the large end of a rectangular funnel 5 at 7, along a seal line A-A, and a tubular neck 9 sealed to the small end of the funnel S. For example, the tube 1 may be a commercial 22VABP4 having an overall panel diagonal dimension of 23.500 inches. The cap 3 comprises a curved viewing faceplate 11 integral with a short cylindrical sidewall 13. The outer surface of the side wall may include the usual maximum dimension rib or mold-match 15 at line 8-8 between the faceplate and the seal line, with the adjacent surfaces sloping away from the rib 15 at selected small angles C and D, as shown in FIG. 2.

The seal at 7 is an integral fused joint in monochrome or black-and-white TV tubes, and fritseal joint in standard color TV tubes having two-piece envelopes. The envelope walls, particularly that of the cap 3, are substantially thicker, and hence, stronger in color tubes than in B & W tubes; and therefore, the implosion protection requirements are substantially higher in B & W tubes. For this reason, the present invention, like other implosion-protection systems, is most applicable to and needed for, but not limited to, B & W tubes.

The envelope cap 3 in FIG. 1 is protected against implosion by means of two superposed steel tension bands 17 and 19 closely surrounding the side wall 13 of the cap 3, preferably centered on the mold-match 15, with the inner band 17 effectively bonded to the glass side wall 13 by an intermediate wrapping of fabric tape 21 impregnated with a thermosetting bonding material, e.g., epoxy resin, which has been cured in situ. The tape 21 should be at least as wide, or wider than, each of the two bands 17 and 19. For example, the tape 21 may be 1 inch wide, and each band may have a width of threefourths inch and a thickness of 0.025 inch. Each band consists of a single steel strap having its ends welded together, with the welded joints on opposite sides of the tube, which produces a symmetrical strain pattern in the glass envelope. The net tension in each of the bands 17 and 19 is preferably about 1,500 pounds. The total compression of the envelope is increased by adding the second band. Satisfactory implosion protection has been obtained with tape 21 impregnated with B-stage (semicured) epoxy resin, which is cured during the band mounting operation described below by heat from the heated bands 17 and 19.

FIG. 3 schematically shows an apparatus and method for mounting each of the two bands 17 and 19 on a rectangular cathode ray tube envelope 2. The apparatus comprises a base plate or block 23 of electrical insulating material formed with a recess or nest 25 having an oval shape slightly larger than the envelope cap 3, and including four (e.g.) upstanding posts 27 and a vacuum cup 29 for supporting the tube 1 during the bonding operation in a position with the funnel 5 up, as shown in FIG. 3. A pair of fixed welding electrodes 31 are mounted adjacent to one side 1a of the tube, and two fixed clamp members 33a and 33b are mounted at each side of the electrodes 31. A movable welding electrode 35 is mounted for movement toward the electrodes 31, and two clamp members 37a and 37b are mounted for movement toward clamp members 33a and 33b, respectively. Means 39 is provided for cutting the band adjacent to the electrode 35. A pair of airoperated clamp-type heating electrodes 41 are used to supply electric heating current to the band.

To apply the first band 17 to the envelope cap 3 of a tube 1, a piece of cloth tape 21, impregnated with semicured B-stage epoxy resin, 1 inch wide, for example, is wrapped around the side wall 13 with the ends overlapped l or 2 inches. Then, the tube 1 is mounted in the nest 25 on the posts 27 and held in place by the vacuum cup 29. A steel strap or band 17, three-fourths inch wide by 0.025 inch thick, for example, from a supply roll (not shown) is threaded into the nest 25 and around the cap 3, between the tube 1 and the side wall of the nest, to the position shown in FIG. 3. Suitable means (not shown) are provided for positioning the band 17 approximately centered on the tape 21. Then, the heating electrodes 41 are clamped to the band 17 in the general locations shown, separated by about twothirds of the periphery of the tube on the side opposite the welding electrodes 31. An electric current of 400-600 amperes passed through the continuous portion of band 17 between the heating electrodes 41 heats that portion to a temperature of 200-250 C. in 5-8 seconds. Then, electrodes 41 are removed, and clamp members 3311 and 37 a are actuated to grip the band 17. The outer end of band 17 is immediately pulled tight to position the band in contact with the tape 21 along the two short sides lb and the bottom long side la of the tube 1. The hot band contacts the tape in l to 1.5 seconds and the curing of the resin starts. At this point, the band 17 has cooled to about 70 percent of its initial temperature. Now, the clamp member 37b is activated to grip the band, and the band is cut by means 39. The welding electrode 35 is now activated to weld the two ends of the band together. Next, the movable elements 37a, 35 and 37b are retracted to release the welded band 21, and the vacuum cup 29 is raised to strip the band off the fixed elements 33a, 31 and 33b. All of the foregoing steps are completed while the band 17 is still hot, and the band shrinkage during subsequent cooling to room temperature subjects the band to a high net tension, preferably about 1,500 pounds. At this point, the resin impregnant in the tape 21 is substantially cured and intimately bonded to the envelope glass and band 17 along more than two-thirds of the periphery of the tube, that is, between the points of attachment of the heating electrodes 41 to the band After the first band 17 has been mounted on the tube 1, as described above, the tube is rotated to position the welded joint in band 17 at the bottom in FIG. 3, and the second band 19 is mounted on top of the first band 17, by the same method as the first band. During this operation, heat is transmitted by the second band 19, through the first band 17, to the portion of the tape not heated (sufficiently) by the first heating of band 17, thereby completing the bonding of the resin impregnant to the glass and the inner band around the entire periphery of the tube.

1 claim:

1. A method of providing implosion-protection means on the side wall portion of a glass cathode ray tube envelope adjacent to the faceplate, comprising the steps of:

a. wrapping a piece of fabric tape, impregnated with an uncured thermosetting bonding material, around said glass envelope portion;

b. positioning a first steel band around said envelope p ortipn and tape;

eating the ma or portion of .said band to a temperature sufficient to cure said bonding material;

d. contacting said tape with said band while hot over the major portion of the periphery of the tube, to cure and bond the major portion of the tape to the glass envelope portion and the band;

e. permanently mounting said band on said envelope by joining the ends of the band together under tension while still hot so that on cooling the band tension is increased to a relatively high value; and

f. then mounting a second steel band on top of said first band in the same manner as said first band, but with the joint located on the opposite side of the envelope, to cure and bond the tape to the envelope and first band along the remaining portion of the tape.

2. A method as in claim 1, wherein said bonding material is B-stage epoxy resin, and said steel bands are heated to a temperature of 200 to 250 C.

3. A method as in claim 1, wherein said major portion of said band is heated by passing an electric current therethrough. 

2. A method as in claim 1, wherein said bonding material is B-stage epoxy resin, and said steel bands are heated to a temperature of 200* to 250* C.
 3. A method as in claim 1, wherein said major portion of said band is heated by passing an electric current therethrough. 